Cell phone and built-in antenna thereof

ABSTRACT

A cell phone including a built-in antenna, the cell phone having a reduced physical size of an antenna element, a decreased weight and satisfying an impact resistance, and suppressing a variation in a dimension caused by mass production and considering an actual use state in which a hand or the like approaches. A dielectric between an antenna element and a ground is a support member of a cyclo-olefin polymer in a plating grade having an impact resistance which is obtained by blending styrene type rubber, polyolefin type rubber (elastomer) or both of them, and the antenna element is constituted by a plating formed on a main surface of the dielectric.

TECHNICAL FIELD

The present invention relates to a cell phone comprising a built-inantenna and the built-in antenna.

BACKGROUND ART

FIG. 6 shows an example (a conventional example 1) of a conventionalcell phone comprising a built-in antenna. In the cell phone according tothe conventional example 1, as shown in FIG. 6, a phosphor bronze plateor the like is plated with nickel for an anticorrosive treatment, andfurthermore, is plated with gold to form an antenna element 2, and theantenna element 2 is stuck to an internal surface of a body rear case 1with a double-sided tape or the like. In FIG. 6, the reference numeral 4denotes a connection part to be connected to a power feeding point 3 ofthe antenna element 2, the reference numeral 5 denotes a circuit boardmounting a radio communication circuit, a liquid crystal display portion(LCD) and various operation keys and the like (not shown), the referencenumeral 6 denotes a ground part of the circuit board 5, the referencenumeral 7 denotes a body front case, the reference numeral 8 denotes abattery, the reference numeral 9 denotes a display window for exposingthe liquid crystal display portion (LCD) of the circuit board 5 to thebody front case 7 side, and the reference numeral 10 denotes a key holefor exposing the operation key of the circuit board 5 to the body frontcase 7 side.

FIG. 7 shows another example (a conventional example 2) of theconventional cell phone comprising a built-in antenna. In theconventional example 2, elements having the same functions as those inthe conventional example 1 shown in FIG. 6 have the same referencenumerals. In the cell phone according to the conventional example 2, asshown in FIG. 7, the same antenna element 2 formed by a metal plate asthat in the conventional example 1 is directly stuck to a block-shapeddielectric 11 having a low dielectric constant and a low dielectricdissipation factor such as PTFE (Polytetrafluoroethylene), or ablock-shaped dielectric 11 such as an LCP (Liquid-crystal polymer) isplated by printing or the dielectric 11 is plated with resin by an MID(Molded Interconnection Device) to constitute a built-in antenna and isdisposed on a ground 6. The MID is a circuit component having athree-dimensional shape which forms a conductive circuit on apredetermined member such as plastic moldings and serves to make thebest of a free three-dimensionality to have a mechanical function or anelectrical function. Recently, the method of directly sticking theantenna element 2 to the block-shaped dielectric 11 such as PTFE(Polytetrafluoroethylene) is unsuitable for the case in which theantenna element 2 is constituted on a side surface or a back face of theblock-shaped dielectric 11 and, particularly, a variation is caused in aheight direction (a clearance between the antenna element 2 and theground 6). For this reason, this method is rarely carried out.

In both the structures of the conventional examples 1 and 2, a power issupplied from the circuit board 5 to the antenna element 2 through theconnection part 4 and a radio wave is radiated from the antenna element2. In order to efficiently radiate the radio wave from the antennaelement 2, it is required that a resonant frequency f0 of the antennaelement 2 ranges within a center frequency frn in a working frequencyband, and a VSWR (voltage standing-wave ratio) is set to be at least 3or less and a return loss {R. L.} is −1.3 dB or less in the workingfrequency band. Moreover, it is also important that a loss caused by thedielectric dissipation factor of the block-shaped dielectric 11 or thelike is lessened. An antenna radiation efficiency required for systemspecifications of a cell phone is varied and is generally −3 dB or moreby putting together a return loss caused by a high VSWR (voltagestanding-wave ratio), a loss caused by the dielectric dissipation factorof the block-shaped dielectric 11 and a loss caused by an approach of anoperator's hand having a high dielectric dissipation factor.

A factor for determining the VSWR (voltage standing-wave ratio) and theresonant frequency of an antenna in a working frequency band includes asize of the antenna element 2, a distance between the antenna element 2and the ground 6 of the circuit board 5 provided thereunder (which isequal to a height or thickness of the block-shaped dielectric 11) and arelative dielectric constant of the block-shaped dielectric 11 providedbetween the antenna element 2 and the ground 6 disposed thereunder. Therelative dielectric constant determines a bandwidth of the antennaelement 2. In order to lessen the loss caused by the block-shapeddielectric 11, a dielectric dissipation factor is to be reduced.

In general, a bandwidth ratio (a bandwidth/a center frequency) requiredfor an antenna of a cell phone is varied depending on the systemspecifications of the cell phone. For example, a PDC (personal digitalcellular) used in Japan has a working frequency band of 810 MHz to 958MHz. If the built-in antenna element 2 is used as an antenna forexclusive receiving, it is sufficient that a bandwidth ratio is 2.2 %(810 MHz to 828 MHz). In case of CDMA (code division multiple access),moreover, a working frequency is 1920 MHz to 2170 MHz. If the built-inantenna element 2 is used as the antenna for exclusive receiving, it issufficient that the bandwidth ratio is 2.8 % (2110 MHz to 2170 MHz).

In case of the CDMA, for example, a microstrip antenna shown in FIGS. 8and 9 may be used as the antenna element 2. If a one-sided short-circuittype microstrip antenna shown in FIGS. 10 and 11 is used, the sameperformance can be obtained with an almost half of a size of themicrostrip antenna shown in FIGS. 8 and 9, for example, which isadvantageous to an area efficiency.

A variation in a distance between the antenna element 2 and the ground 6which is caused by a tolerance in an assembly is one factor fordetermining the resonant frequency of the antenna element 2. In case ofthe conventional example 1 in which the antenna element 2 is stuck tothe body rear case 1, a sticking position is determined on the basis ofa fitting surface of the body front case 7 and the body rear case 1which gives a fine appearance. Therefore, the variation in the distancebetween the antenna element 2 and the ground 6 depends on precision indimensions of the body front case 7 and the body rear case 1 and isslightly great, that is, approximately 0.3 mm.

In case of the conventional example 2 in which the antenna element 2 isconstituted on the block-shaped dielectric 11 and is disposed on theground 6, moreover, the variation in the distance between the antennaelement 2 and the ground 6 is approximately 0.1 mm to be a generaltolerance. In consideration of these matters, it is necessary toconstitute the antenna and to optimally select characteristics of arelative dielectric constant and a dielectric dissipation factor of adielectric. If not so, there is a problem in that a set resonantfrequency of the antenna is varied, and furthermore, a variation in anantenna performance is increased and speech quality is not stabilized.

More specifically, the conventional example 1 (FIG. 6) will be taken asan example. In the case in which the antenna element 2 is stuck to thebody rear case 1, the sticking position is determined on the basis ofthe fitting surface of the body front case 7 and the body rear case 1which gives a fine appearance. Therefore, an assembly error between theantenna element 2 and the ground 6 is ±0.3 mm as described above. Therewill be considered the case in which the antenna element 2 isconstituted by an area of 62.9 mm×62.9 mm (3956.4 mm²) as shown in FIG.12, for example. A relative dielectric constant between an antenna and aground is 1.0 because air is only present. A relationship between aresonant frequency f (MHz) and a VSWR (voltage standing-wave ratio) isshown in FIG. 13. FIG. 13 shows both the case in which a clearance hbetween the antenna element 2 and the ground 6 is implemented to be 1.2mm which is a dimension for a design (see a solid curve) and the case inwhich the distance h is 0.9 (=1.2−0.3) mm in consideration of the factthat an assembly error is ±0.3 mm as described above (see a brokencurve). As shown in FIG. 13, the resonant frequency f is 2140 MHz withthe distance h=1.2 mm, while the resonant frequency f is shifted to 2187MHz with the distance h=0.9 mm. While the VSWR obtained when a band endfrequency f is 2110 MHz is 2.1 with the distance h=1.2 mm (that is, areturn loss {R. L.}=−0.6 dB), for example, it is increased to 5.8 withthe distance h=0.9 mm (that is, a return loss {R. L.}=−3.0 dB) so that areflection loss of −2.4 dB is caused. For this reason, mass productioncannot be achieved.

On the other hand, for example, in the case in which ceramics particlesof BaTiO₃ containing Sr in a weight ratio of 83% and a polyolefin typepolymer matrix in a weight ratio of 17% are mixed to be a compositematerial as the dielectric having the structure according to theconventional example 2 (for example, Japanese Patent ApplicationLaid-Open No. 6-140830 (1994)), a relative dielectric constant is 15.8.By using the dielectric, a volume can be reduced to be 10% or less ascompared with the conventional example 1 shown in FIG. 6 (thedesignation Pb in FIG. 14) as is indicated by the designation Pa of FIG.14 so that a size of the antenna 2 can be decreased by a wavelengthshortening effect produced by the relative dielectric constant of thedielectric.

In this case, however, a bandwidth ratio with a VSWR of 3 or less is1.1% (not shown) and the VSWR is 12.4 at a band end of 2110 MHz and 2170MHz (that is, a return loss {R. L}=−5.6 dB), and therefore, the massproduction cannot be achieved.

In this case, if the antenna element 2 is constituted with an area of18.2 mm×18.2 mm as shown in FIG. 15, for example, a relationship betweenthe resonant frequency f (MHz) and the VSWR (voltage standing-waveratio) shown in FIG. 16 is obtained. An error in a height direction (h)of the antenna element 2 shown in the structure of FIG. 15 is ±0.1 mm.FIG. 16 shows the case in which the clearance h between the antennaelement 2 and the ground 6 is implemented to be 1.2 mm which is adimension for a design (see a solid curve) and the case in which thedistance h is 1.1 (=1.2−0.1) mm (see a broken curve). As shown in FIG.16, the resonant frequency f is 2140 MHz with the distance h=1.2 mm (astate in which shielding is not carried out with a hand 13: see thesolid curve), while the resonant frequency f is shifted to 2163 MHz withthe distance h=1.1 mm (see the broken curve). While the VSWR obtainedwhen the band end frequency f is 2110 MHz is 12.4 with the distanceh=1.2 mm (that is, a return loss {R. L.}=−5.6 dB which is not shown),for example, it is increased to 44.6 with the distance h=1.1 mm (thatis, a return loss {R. L.}=−10.7 dB which is not shown) so that areflection loss of −5.1 dB is caused. For this reason, the massproduction cannot be achieved.

Moreover, a cell phone is often held with the hand 13 for use as shownin FIG. 17. Therefore, a part of the hand 13 such as an index fingercovers a portion 1 a in which the antenna 2 of the body rear case 1 isprovided (a portion shown in a broken line of FIG. 17) so that the sameportion is shielded in some cases. With the hand 13, a preset resonantfrequency of the antenna is shifted in some cases. In these cases, thereis a problem in that an antenna performance is deteriorated in a workingfrequency band, resulting in unstable speech quality as shown in aone-dotted chain curve L1 of FIG. 16.

Furthermore, if a physical size of the built-in antenna element 2 isexcessively reduced by increasing the relative constant dielectric of adielectric block, a current flowing to the antenna element 2concentrates. Consequently, there is a problem in that a loss caused bythe hand 13 having a great dielectric dissipation factor is increasedand an antenna performance is thus deteriorated, resulting ininstability of the speech quality.

The built-in antenna element 2 of the cell phone has a twofold modelshown in FIG. 18 in addition to the shape illustrated in FIG. 6 or 7. Inthe twofold model, a cell phone body can be bent to be folded double ina hinge portion 18. In this case, the antenna element 2 is mounted byfixing an attachment member 2 b shown in FIG. 18 to the circuit board 5with a screw 14. In this case, there is a problem in that a great impactis given to a portion in which the antenna 2 is provided so that theantenna element 2 might be broken to deteriorate the antennaperformance, resulting in unstable speech quality if dropping is carriedout with the attachment portion of the antenna element 2 turneddownward.

In some cases, the built-in antenna element 2 of the cell phone issoldered onto the circuit board 5 mounting a radio part by reflow inorder to suppress a deterioration in the antenna performance which iscaused by a reduction in a process and a variation in an attachmentposition. A dielectric resistant to the reflow includes an LCP(Liquid-crystal polymer). However, there is a problem in that the LCPhas a great specific gravity and is therefore unstable for a cell phonerequiring a reduction in a weight.

DISCLOSURE OF THE INVENTION

It is an object of the present invention to solve the problems describedabove and to properly reduce a physical size of an antenna element, todecrease a weight and satisfy an impact resistance, to suppress avariation in a dimension in mass production, and to set speech qualityto a level having no problem in consideration of an actual use state inwhich a hand or the like approaches in a built-in antenna of a cellphone.

According to a first aspect of a cell phone in accordance with thepresent invention, a cell phone comprises a built-in antenna having asupport member of a dielectric (15) between an antenna element (2 a) anda ground (6), wherein the dielectric (15) is constituted by acyclo-olefin polymer blending styrene type rubber, polyolefin typerubber or both of them, and the antenna element (2) is constituted by aplating formed on a main surface of the support member.

Consequently, an antenna element having a proper size and a highperformance can be formed in the cell phone and a necessary bandwidthratio can be obtained, and speech quality is not greatly influenced evenif a variation in an assembly of mass production and an influence of ahand in actual use are taken into consideration. Moreover, the styrenetype rubber, the polyolefin type rubber or both of them is/are blendedwith the cyclo-olefin polymer. Therefore, a sufficient impact strengthis obtained and a clearance between the antenna element and an innerpart of a housing does not need to be taken excessively. Thus, adimension of an appearance of the cell phone can be more reduced thanthat in the case in which a material having a small impact strength isto be used. Furthermore, a density is low. Consequently, a weight of theantenna element can be reduced, and furthermore, a great contribution toa reduction in a weight of the cell phone can be made.

It is desirable that the dielectric (15) should be a molded productusing the cyclo-olefin polymer in a plating grade having a lowdielectric constant and a low dielectric dissipation factor by blendingelastomer to be polyolefin type rubber.

It is further desirable that the ground should be constituted by apredetermined shield box, and the shield box should include a moldedproduct using the cyclo-olefin polymer in a plating grade and a platingformed on the molded product and should be formed integrally with theantenna element.

Objects, features, aspects and advantages of the present invention willbe more apparent from the following detailed description and theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing an example of an internal structureof a cell phone according to a first embodiment of the presentinvention.

FIG. 2 is a perspective view showing another example of the internalstructure of the cell phone according to the first embodiment of thepresent invention.

FIG. 3 is a perspective view showing a built-in antenna of the cellphone according to the first embodiment of the present invention.

FIG. 4 is a chart showing a relationship between a resonant frequency ofthe built-in antenna and a VSWR in the cell phone according to the firstembodiment of the present invention.

FIG. 5 is a chart showing a relationship between a dielectricdissipation factor and an antenna radiation efficiency in the built-inantenna of the cell phone according to the first embodiment of thepresent invention.

FIG. 6 is an exploded perspective view showing an example of an internalstructure of a conventional cell phone.

FIG. 7 is an exploded-perspective view showing another example of theinternal structure of the conventional cell phone.

FIG. 8 is a perspective view showing an example of a built-in antenna ofthe conventional cell phone.

FIG. 9 is a sectional view showing the example of the built-in antennaof the conventional cell phone.

FIG. 10 is a perspective view showing another example of the built-inantenna of the conventional cell phone.

FIG. 11 is a sectional view showing another example of the built-inantenna of the conventional cell phone.

FIG. 12 is a perspective view showing a built-in antenna of a cell phoneaccording to a conventional example 1.

FIG. 13 is a chart showing a relationship between a resonant frequencyof the built-in antenna and a VSWR in the cell phone according to theconventional example 1.

FIG. 14 is a chart showing a relationship between a relative dielectricconstant of a dielectric between an antenna element and a ground and avolume of an antenna.

FIG. 15 is a perspective view showing a built-in antenna of a cell phoneaccording to a conventional example 2.

FIG. 16 is a chart showing a relationship between a resonant frequencyof a built-in antenna and a VSWR in the cell phone according to theconventional example 2.

FIG. 17 is a view showing a state in which a hand covers a position onwhich the built-in antenna is mounted.

FIG. 18 is a perspective view showing a cell phone of a twofold model,which is partially taken away.

BEST MODE FOR CARRYING OUT THE INVENTION 1. FIRST EMBODIMENT

In a built-in antenna of a cell phone, generally, the inventor examinedconditions of a characteristic required for a material of a dielectricbetween an antenna element and a ground. As a result, the followingitems (1) to (6) can be given.

-   -   (1) A relative dielectric constant is equal to or smaller than        3,    -   (2) a dielectric dissipation factor is low, that is, 0.0002 or        less,    -   (3) plating can be carried out by an MID (Molded Interconnection        Device) or a printing method,    -   (4) an impact strength is at least equal to or greater than that        (30J) of ABS (Acrylonitrile-butadiene-styrene) which is        generally used in a cell phone,    -   (5) a heat resistance to solder reflow is held, and    -   (6) a density is low.

The inventor examined a material which can be used as an antenna element(the designation 2 a in FIGS. 1 and 2) of a built-in antenna. As aresult, it was found that materials listed in the following Table 1 canbe given. TABLE 1 Relative Dielectric dielectric dissipation Impactconstant factor Density HDT(° C.) strength DefectPTFE(Polyterafluoroethylene) 2.1 0.0002 2.20 51 15.5 Plating property,Workability PP(Polypropylene) 2.2 0.0002 0.90 52 4.9 Plating propertyPS(Polystyrene) 2.4 0.0002 1.00 82 1.4 Chemical resistance, Platingproperty S-PS(Syndiotactic-polystyren) 2.4 0.0003 1.10 220 1.0 Platingproperty, Impact strength LCP(Liquid-cryatal polymer) 2.8 0.002 1.80 2204.0 Density COP(Cyclo-olefin polymer) 2.3 0.0001 1.00 123 35.0 NoneProduct described in Japanese 15.8 0.00044 2˜3.5 Unknown Unknown DensityPatent Application Laid-Open No. 6-140830 (1994)

Only a COP (Cyclo-olefin polymer) satisfies the conditions (1) to (6)described above. In the cell phone according to the present embodiment,for example, polyolefin type rubber is blended with a COP (Cyclo-olefinpolymer) 15 in a block-shaped plating grade to obtain a plating gradeand a dielectric is caused to have an impact resistance, a lowdielectric constant and a low dielectric dissipation factor, and the COP15 plated with resin by an MID (Molded Interconnection Device) isapplied to be an antenna element 2 a as shown in FIGS. 1 and 2. There isemployed a structure in which the block-shaped COP (Cyclo-olefinpolymer) 15 is fixed to a ground 6 of a circuit board 5 with a screw 14as shown in FIG. 1 or is fixed to the ground 6 of the circuit board 5 bysolder reflow as shown in FIG. 2.

FIG. 3 shows the built-in antenna of the cell phone according to thefirst embodiment of the present invention. In the built-in antenna ofthe cell phone, it is possible to reduce a size by applying the COP as amaterial of a dielectric. As shown in FIG. 3, therefore, a main surfaceof the antenna element 2 a (that is, a main surface of the COP 15) isset to have a size of 44.2 mm×44.2 mm (an area=1953.6 mm²) and is set tohave an area of 50% or less as compared with the conventional example 1(3956.4 mm²).

It is more desirable that a structure of a one-sided short-circuit typemicrostrip antenna (see FIGS. 10 and 11) should be employed for theantenna element 2 a. The reason is that it is possible to obtain anantenna in which the main surface of the antenna element 2 a (the mainsurface of the COP 15) has the same performance with an approximatelyhalf area (that is, an approximately quarter of the area in theconventional example 1). In the case in which the antenna is mounted onthe cell phone, therefore, a sufficient performance can be retained witha smaller area, which is advantageous.

A bandwidth ratio of the antenna element 2 a using the COP 15 in theplating grade as the dielectric is 3% and satisfies a bandwidth ratio of2.8% or more to be a requirement, which is not shown in the Table 1.

A relationship between a resonant frequency f (MHz) of the antennaelement 2 a and a VSWR (voltage standing-wave ratio) is obtained asshown in FIG. 4. An error in a height direction (h) of the antennaelement 2 a in the structure of FIG. 3 is 0.1 mm. Therefore, FIG. 4shows three states including the case in which a clearance h between theantenna element 2 a and the ground 6 is implemented to be 1.2 mm whichis a dimension for a design (see a solid curve), the case in which thedistance h is 1.1 (=1.2−0.1) mm (see a broken curve), and the case inwhich the distance h is 1.2 mm and holding and shielding are carried outwith a hand 13 as shown in FIG. 17 (a one-dotted chain curve L1: see thefollowing).

As shown in FIG. 16, in the case in which the antenna element 2 a is tobe formed on the main surface of the COP 15 as in the presentembodiment, the resonant frequency f is 2140 MHz with the distance h=1.2mm (a state in which the shielding is not carried out with the hand 13:see a solid curve) and is shifted to 2155 MHz by ±15 MHz with thedistance h=1.1 mm (see a broken curve). However, the bandwidth ratio iscomparatively high, that is, 3%. For this reason, when a band endfrequency f is 2110 MHz, for example, the VSWR is 2.8 (that is, a returnloss {R. L}=−1.1 dB) with the distance h=1.2 mm, and is increased to 4.0(that is, the return loss {R. L}=−1.9 dB) with the distance h=1.1 mm anda reflection loss is reduced to be −0.8 dB.

FIG. 5 shows a relationship between a dielectric dissipation factor andan antenna radiation efficiency. The dielectric dissipation factor ofthe COP (Cyclo-olefin polymer) 15 is set to be very small, that is,approximately 0.0001. Consequently, a deterioration in the antennaradiation efficiency is approximately −0.1 dB. In consideration of avariation in an assembly which is caused by mass production, thedielectric dissipation factor is approximately 10⁻². Therefore, it ispossible to obtain an antenna radiation efficiency of −2.0 dB at theworst in FIG. 5.

In the case in which the COP 15 and the antenna element 2 a in FIG. 3are used, moreover, the relationship between the resonant frequency fand the VSWR is obtained as shown in a one-dotted chain line L2 of FIG.4 when a finger 13 of a hand approaches in use of the cell phone asshown in FIG. 17 (assuming that the hand 13 has a relative dielectricconstant of 50 and a dielectric dissipation factor of 0.5 and aclearance between the ground 6 and the hand 13 is 1 mm). Since theantenna element 2 a shown in FIG. 3 has a relative dielectric constantof 2.3 (Table 1), a size of the antenna element 2 a is greater than thatof the antenna element 2 (18.2 mm×18.2 mm) shown in FIG. 15.Consequently, it is apparent that an influence of the hand 13 is smalland the resonant frequency is 2137 MHz (see a one-dotted chain line L2in FIG. 4) which is shifted from the resonant frequency of 2140 by 3 MHzin the case in which the shielding is not carried out with the hand 13,and furthermore, a power to be absorbed by the hand 13 is −0.6 dB.

On the other hand, in the case in which the relative dielectric constantis 15.8 (see FIGS. 15 and 16), the antenna element 2 is small and a highfrequency current flowing to the antenna element 2 is blocked by thehand 13 (FIG. 17). As shown in FIG. 16, consequently, the resonantfrequency is shifted to 2126 MH by 14 MHz, and furthermore, the powerabsorbed by the hand 13 is −6.2 dB.

In consideration of these matters altogether, the loss is −2.6 dB (=−1.9dB−0.1 dB−0.6 dB) at the worst by the use of the antenna element 2 aaccording to the present embodiment to satisfy the condition that anantenna radiation efficiency is to be −3.0 dB or less by puttingtogether the assumed bandwidth ratio of the built-in antenna element 2a, that is, 2.8% or more, an in-band reflection loss obtained inconsideration of a variation in an assembly which is caused by the massproduction, a loss of a dielectric and a loss of a hand.

By the use of the antenna element 2 a utilizing the COP 15 according tothe present embodiment, moreover, there is no problem even if theantenna element 2 a is fixed to the ground 6 with the screw 14 as shownin FIG. 1 or is directly fixed to the board 5 by solder-reflow as shownin FIG. 2 because of an impact strength which is equal to or greaterthan that of ABS (Acrylonitrile-butadiene-styrene) to be usually used inthe internal structure of the cell phone.

Furthermore, the same value as values in other portions can be used fora clearance between an internal surface of a housing (corresponding tothe body rear case 1 in FIGS. 6 and 7) of the cell phone and the antennaelement 2 a, and a size in an appearance can also be reduced as comparedwith use of a material having a small impact strength.

Since a density is comparatively low, that is, 1.0 for a materialcharacteristic of the COP 15, moreover, a weight of the antenna element2 a can be reduced and a great contribution to a reduction in a weightto be an indispensable item of the cell phone can be made.

As described above, there is employed a structure in which the antennaelement 2 a is plated by the MID on the COP (Cyclo-olefin polymer) 15 inthe plating grade in which a relative dielectric constant and adielectric dissipation factor are optimum in the built-in antennaportion of an optimum cell phone. Therefore, an antenna performance canbe enhanced and is not remarkably deteriorated with a variation in anassembly which is caused by mass production, and furthermore, theinfluence of the hand can also be relieved in actual use. Consequently,the antenna performance is stabilized and speech quality is made stable.As described above, moreover, the impact strength of the antenna element2 a is great. Therefore, restrictions on attachment can be lessened inthe housing of the cell phone and the mass production can suitably beachieved. Furthermore, it is possible to greatly contribute to areduction in a weight to be the indispensable item of the cell phonebased on the material characteristic of the COP 15.

While the polyolefin type rubber (elastomer) is blended with the COP 15to have the plating grade and a material having an impact resistance, alow dielectric constant and a low dissipation factor is applied as thedielectric in the present embodiment, it is also possible to apply amaterial obtained by blending styrene type rubber with the COP 15 whichis set into the plating grade and has an impact resistance, a lowdielectric constant and a low dielectric dissipation factor, forexample.

2. SECOND EMBODIMENT

While the COP (Cyclo-olefin polymer) 15 to be a block-shaped dielectricin the plating grade which is subjected to the resin plating by the MID(Molded Interconnection Device) is applied as the antenna element 2 a inthe first embodiment, the same effects as those in the first embodimentcan be obtained even if the block-shaped COP (Cyclo-olefin polymer) 15subjected to the resin plating by a printing method is applied in placeof such a structure. Also in this case, it is preferable that theantenna element 2 a should be fixed onto the ground 6 of the circuitboard 5 as shown in FIGS. 1 and 2.

3. THIRD EMBODIMENT

While the antenna element 2 a is formed on the COP 15 in the platinggrade and is fixed to the ground 6 provided on the circuit board 5 ineach of the embodiments, for example, it is also possible to employ sucha structure that a shield box for shielding a noise in which the ground6 is to be provided is formed by the COP (Cyclo-olefin polymer) 15 inthe plating grade and the antenna element 2 a and the shield box (ground6) are plated by an MID (Molded Interconnection Device), a printingmethod or the like in the case in which the circuit board 5 in which theground 6 is not formed is covered with the shield box from above inFIGS. 1 and 2 and a metal for shielding of the shielding box also servesas the ground 6. Thus, it is not necessary to combine the shield box andthe antenna element 2 a as separate members. Therefore, precision in anassembly can be prevented from being varied and it is sufficient thatonly precision in molding is considered. Accordingly, the clearance (thedesignation h in FIG. 3) between the antenna element 2 a and the shieldbox (ground 6) is further stabilized and a variation in an assemblycaused by mass production can be reduced so that an antenna performancecan be stabilized and speech quality can be made stable.

While the present invention has been described in detail, the abovedescription is only illustrative in all aspects and the presentinvention is not restricted thereto. It is understood that numerousvariants which are not illustrated can be supposed without departingfrom the scope of the present invention.

1-10. (canceled)
 11. A cell phone comprising: a built-in antenna havinga support member of a dielectric between an antenna element and aground, wherein said dielectric is constituted by a cyclo-olefin polymerblending styrene type rubber, polyolefin type rubber or both of them,and said antenna element is a plating formed on a main surface of saidsupport member.
 12. The cell phone according to claim 11, wherein saiddielectric is obtained by using said cyclo-olefin polymer blendingpolyolefin type rubber.
 13. The cell phone according to claim 11,wherein said ground is constituted by a predetermined shield box, andsaid shield box includes a support member using said cyclo-olefinpolymer in a plating grade and a plating formed on said support member,and is formed integrally with said antenna element.
 14. The cell phoneaccording to claim 11, wherein said plating is formed on a main surfaceof said support member by an MID.
 15. The cell phone according to claim11, wherein said plating is formed on a main surface of said supportmember by printing.
 16. A built-in antenna of a cell phone which isbuilt in said cell phone, the built-in antenna comprising: a supportmember of a dielectric between an antenna element and a ground, whereinsaid dielectric is constituted by a support member of a cyclo-olefinpolymer blending styrene type rubber, polyolefin type rubber or both ofthem, and said antenna element is a plating formed on a main surface ofsaid support member.
 17. The built-in antenna of a cell phone accordingto claim 16, wherein said dielectric is obtained by using saidcyclo-olefin polymer blending polyolefin type rubber.
 18. The built-inantenna of a cell phone according to claim 16, wherein said ground isconstituted by a predetermined shield box, and said shield box includesa support member using said cyclo-olefin polymer in a plating grade anda plating formed on said support member, and is formed integrally withsaid antenna element.
 19. The built-in antenna of a cell phone accordingto claim 16, wherein said plating is formed on a main surface of saidsupport member by an MID.
 20. The built-in antenna of a cell phoneaccording to claim 16, wherein said plating is formed on a main surfaceof said support member by printing.